In the conventional art, a gas barrier film having a thin film of metallic oxide such as aluminum oxide, magnesium oxide and silicon oxide formed on the surface of a plastic substrate and film has been extensively used to package the products that require interception of various types of gases such as vapor and oxygen, as well as to package the foods and industrial products to prevent them from being deteriorated. In addition to packaging purposes, the gas barrier film has also been used as a substrate for a liquid crystal device, solar battery and organic electroluminescent device (hereinafter referred to as “organic EL”) or the like. An aluminum foil is widely used as a packaging material in this field. However, the problem with this material is that effective method for waste disposal has not yet been found out after use, and the contents packaged in the aluminum foil cannot be identified from outside because it is basically non-transparent. Further, transparency is very important when used as a display material, and an aluminum foil completely fails to meet this requirement.
The substrate made of a polyvinylidene chloride resin or a copolymer resin made of vinylidene chloride and other polymer, or a material with gas barrier function provided by coating these vinylidene chloride-based resins on a polypropylene resin, polyester resin and polyamide resin is extensively used as a packaging material in particular. However, since chloride-related gases are produced in the process of incineration, this material is seen as creating an environmental problem. Further, its gas barrier function is not always satisfactory, and this material cannot be used in the field wherein a high degree of barrier function is essential.
The transparent substrate that is applied to the liquid crystal device and organic EL device to a greater extent. In addition to the requirements for less weight and greater size, sophisticated requirements such as long-term reliability, freedom in the shape and display on a curvature are being imposed on such a substrate. Thus, such a film substrate as a transparent plastic is coming into use, instead of a glass substrate that is vulnerable to cracks and is difficult to increase the space. For example, the Unexamined Japanese Patent Application Publication No. H2-251429 and Unexamined Japanese Patent Application Publication No. H6-124785 disclose an example of using a high molecular film as a substrate of the organic electroluminescent device.
However, the substrate such as a transparent plastic has a bas barrier function inferior to that of glass. For example, when a substrate of inferior gas barrier function is used as a substrate of the organic electroluminescent device, the organic film will be deteriorated by permeation of vapor and air, with the result that light emitting function or durability will be lost. Further, when a high molecular resin substrate is used as an electronic device substrate, oxygen will pass through the high molecular resin substrate to enter the electronic device, wherein oxygen will spread and deteriorate the device. Further, the degree of vacuum required inside the electronic device cannot be maintained.
Such problems have been left unsolved.
One of the known techniques to solve the aforementioned problems provides a method of producing a gas barrier film substrate by forming a thin film of metallic oxide on a resin film. Known gas barrier films used as a packaging material or liquid crystal display device are exemplified by the gas barrier film formed by vapor deposition of silicon oxide on a plastic film (e.g., Patent Document 1) and the film formed by vapor deposition of aluminum oxide thereon (e.g., Patent Document 2).
One of the methods for meeting the requirements for a high degree of vapor cutoff property proposed so far is the technique of producing a gas barrier film formed by alternate lamination of a compact ceramic layer and a flexible polymer layer for reducing the external impact (Patent Documents 3 and 4).
However, despite the description of the Patent Documents 3 and 4, there are problems with the adhesion between the substrate and ceramic film (layer), and stability against chronological change in particular. The barrier function is comparatively satisfactory in the initial phase but tends to be reduced in repeated thermal tests. Thus, there has been a intense demand for a gas barrier film characterized by superb flexibility and excellent barrier function.
Patent Document 1: Unexamined Japanese Patent Application Publication No. S53-12953 (Tokkosho)
Patent Document 2: Unexamined Japanese Patent Application Publication No. S58-217344 (Tokkaisho)
Patent Document 3: U.S. Pat. No. 6,268,695 (Specification)
Patent Document 4: U.S. Pat. No. 6,413,645 (Specification)